Nonsvnchronous motor



Patented June 28, 1927.

UNITED STATES VALBE A. '.EYNN, OF ST. LOUIS, MISSOURI.

NONSYNCHRONOUS MOTOR.

Application filed October 22, 1926. Serial No. 143,429.

My invention relates to polyphase induction motors with power factor control and particularly to an improved method and means Vfor starting such motors.

The power factor of a polyphase induction motor can be placed under control by producing at least part of the revolving field of the machine from the secondary. This involves the introduction into polyphase exciting circuits located 'on the secondary of auxiliary or excitingpolyphase currents of proper phase and of the slip frequency of the ino-toi'. In some cases these auxiliary currents are derived from the line directly and are` therefore, originally of line frequency. l/Vhen so derived it is necessary to provide for the conversion of the frequency of said currents from line to slip frequency and this may be donc by means of a frequency converter embodied in the inotor or separate therefrom. Particularly when the frequency converter is embodied in the motor and the latter is of the slipring type, it will be found thatat the monient of starting such a machine unwelcome and destructive sparking will generally take place between the commutator and brushes forming a part of the frequency converter embodied in the motor. This sparking is practically independent of whether or not the commutator brush circuits are closed at starting and is due, at very slow speeds, almost entirely to the voltage or voltages generated in those w1turns of the comniuted winding which are shortcircuited by therindividual brush-es resting on the commutator. In order to overcome this drawback I have conceived the idea of lifting commutator brushes off the commutator during the starting operation and dropping them back into contact with said commutator after the machine has reach-ed its normal speed or a speed beginning to approach the normal, generally speaking, a speed at which the resultant of the voltages generated iii the coils undergoing commutation and of the reactance voltages of said coils has diminished to a valu-e which will not cause harmful sparking.

The objects and features of this invention will more clearly appear from the detailedV description taken in conjunction with the accompanying drawing and will be pointed out in the claims.

Referring to the drawing which' illustrates a two-pole embodiment of my invention and which shows `a three-phase slipring motor, the primary, here the stationary member, carries a three-phase winding'2 adapted to be connected to the mains 26, 27, 28 by means of the switch 25.V The"secondary, here the rotor, is shownbyv way yofV example as carrying two windings, a three- Vphase working winding 10 connected to the sliprings 11, 12, 13 and through-brushes cooperating with said sliprings to the starting resistances 19, 20, 21, and an exciting winding in the form of a commuted winding 9 with which cooperate the brushes-3, 4,. 5 held in brush holders each ofwhich is pivoted on a pin 29. The brushes 3, 4t, 5

are shown asresting directly on the circle 9 representing the cominuted winding, in practice a commutator would, of cou-rse, be interposed. These commutator brushes are connected to the adjustable ratio threephase transformer 24, the primaries: of which areconnected to the mains. The starshaped member 22 of the 'controllerV is adapted to interconnect the resistances 19, 20, 21, thus completing the circuits 'of the Working Winding 10. In the position shown in the figure the member 22 is shown shortcircuiting the secondary .working winding 10. Each of the brush holders holding the c ommutator brushes is provid-ed with ahornlike projection 6,k 7 8 of insulating material.

A ring-Shaped member 14 movable concentrically with the secondary member` of the motor, and, therefore, with the commutator carried by said member, is' provided with elongated projections 15, 16, 17 adapted to cooperate with the horn-like projections on the brush holders so as vto cause the brush holders to pivot on their supporting pins 29 and thus lift the brushes 3, 4,15 ofi' the commutator or off the winding 9; In 'the arrangement shown in the figure, the member 14 must be revolved counterclockwise in drive the member 14 which is adapted to cooperate with the commutator brush holders of the motor. The resistances 19, 20, 21 may, of course, be replaced by any kind of impedance.

In vthe ligure the exciting winding t) is shown between the working winding l() on the secondary and the wor-king windingr2 on the primary. This location of the winding 9 has been selected merely 'for 'the Ysake of a more convenient and more clear illustration of the features of this invention. As a mattei of fact it will usually be preferable to locate the secondary working winding 10 between the primary and the other 'winding on the secondary, as is now well raider-stood, but the present invention is applicable rcgardless ofthe relative positions of these threewindings and also applies to machines of this type in which the secondary working and the secondary exciting circuits are contrived in one and the same winding on the secondary and whether or not means are provided for excluding working currents from the secondary exciting circuits.

Referring to the operation of the machine, the brushes 3, 4L, 5 are so located with refer" ence to the phases of the winding` 2 on the primary that when the machine is in operation and the commutator brushes are con- .nected to the transformer 24:, the auxiliary currents introduced into the secondary 9 do compensate the'machine, that is, do improve its power factor. lith the brushes 3, t, 5 in the correct position and with the member 22 shortcircuiting the secondary working winding 10, the member 1e is located as shown in the figure, namely out of contact with the brush holder horns and so that a movement of the handle 23 `in a clockwise direction will bring the projections 15, y16, 17 of the ring 14 into contact with the horns 6, 7, 8 of the brush holders and lift the brushes out of contact .with `the commuted winding 9 after the handle 23 has moved through more or less of an arc. Thus, .the brushes 3, 4, 5 may be liftedbefore .themem ber 22 leav-es `those contacts which short circuit-the winding or after saidmember has left the contacts in question and has inserted more or less resistance into the circuits including the winding .10, but `in all cases the brushes 3, 4c, 5 must be lifted olf when the winding 10 is on open circuit or when an amount of resistance is included in circuit with said winding which causes the motor speed to fall considerably below the synchronous.

In order to start the machine the handle 23 is moved in a. clockwise directionuntil the circuits of the winding 10 are interrupted or until that amount of resistance is inserted into the circuits of said winding which corresponds to the desired starting torque. ,At such time the projections 15, 16, 17 will be in operative contact with the horns 6, 7, 8 and the brushes 3, 1, 5 will be lifted olf the commuted winding 9. Theprimary winding 2 may now be connected to the mains by closing the switch 25 and the machine accelerated by moving the handle 23 in a counterclockwise direction until lthe position shown in thelignre is reached. At such time, if not before, the projections 15, 16, 17 break operative connect-ion with the horns (i, 7, 8, the brushes 3, 11, 5 contact with the winding 9 and the power factor of the machine is placed under control and improved.

ln the case of slipring induction motors, arrangements are often made to shortcircuit the secondary working winding independently of the sliprings after the machine has been brought up to speed and to then lift the slipring brushes olf the sliprings. Such an arrangement can, of course, be combined with the one here described without departing from the spirit of this invention.

Throughout this specification the term primary member is applied to that member which carries the windings connect-ed to the supply, which windings carry the line working currents, and whether or not these primary windings produce the revolving tlux of the motor, which flux always revolves synchronously with respectfto the primary member. The other member is referred to as secondary whether or not it carries a winding or windings .which produce all or a part of the'revolving flux.

lt is well known that any motor can be operated as a generator, provided it be driven by a prime mover at a suitable speed and it is also generally recognized that nonsynchronous polyphase motors are no exception to'this rule.

llChe Varrangement here shown may be applied to nonsynchronous generators with advantage, in case the latter are connected to the mains at speeds materially differing from the synchronous, at which time sparking at Mthe commutator brushes will occur unless the latter are lifted off and not released until the synchronous or a near synchronous speed has been reached.

This invention is also applicable to single phase slipring induction motors started as split-phase motors. rlhe fact that in single phase motors phase compensation is achieved in a totally different manner, namely by inj eating into the always presentexciting circuit on the secondary an auxiliary voltage intended to modify the phase of the speed iield of the machine, is quite immaterial. Such motors carry a commuted winding on the secondary kmember and if the brushes cooperating with said winding are left down at starting while resistances are inserted into the secondary vicious sparking may result.

It is clear that various changes may be made in the details of this disclosure with- Die out departing from the spirit of this invention, and it is, therefore, to be understood that this invention is not to be limited to the specific details here shown and described. ln the appended claims l am to cover all the modifications Which are Within the scope of my invention. l

What I claim is:

l. A non-synchronous alternating current motor, having a commuted and a Working winding on its secondary, brushes cooperating with the commuted Winding, means for introducing impedance into the Working winding on the secondary, means for raising the brushes off the commuted Winding, and an interlocking device for the two aforesaid means adapted to lift the brushes Off the commuted Winding some time after the impedance introducing means has been set in motion to increase the impedance of the secondary Working Winding.

2. A non-synchronous alternating current motor, having working and exciting circuits on the secondary, frequency transforming means in circuit with the secondary exciting circuits and including a commutator and cooperating brushes normally held in contact with said commutator, means for introducing impedance int-o the Working circuits on the secondary, means for raising the brushes olf the coinmutator, and an interlocking device for the two aforesaid means adapted to allow the brushes to rest on the commutator When the secondary Working circuits are shortcircuited and to move the brushes out of contact With the commutator When a certain amount of impedance is introduced into the secondary Working circuits.

3. A non-synchronous alternating current motor, having Working and exciting circuits on the secondary, frequency transforming means in circuit With the secondary exciting circuits and including a commutator and cooperating brushes normally held in contact with said commutator, and means for holding the brushes off the commutator at starting.

4;. The method of operating a phase compensated alternating current induction motor having a commutator and cooperating brushes, comprising, starting the machine by impressing an alternating voltage on the.

primary and introducing impedance into its secondary member, decreasing said impedance and shortcircuiting the secondary member, concurrently interrupting the compensating circuits at starting by lifting the brushes off the winding with Which they cooperate, and reestablishing cooperative relation between the commuted Winding and the brushes after the machine has reached a suticient speed. Y

in testimony whereof I afIiX my signature this 20th dayof October', 1926.

VALRE A. FYN N. 

